Cathode ray tube



Oct. 31, 1939.

L KLATZOW 2,178,233

CAIHODE RAY TUBE Filed June 11, 1957 INVENTOR L' KLATZOW ATTO RN EY amOscar, 1939 2,178,233

U ITED STATES PATENT OFFICE 2.11am Y Leonard Klatacw, Bayswater, London,England,

anlgnortolilecttic thlllatcallndultriqlllmited, Hayes, lllddleaex,England, a British oom- P Application June 11, 1837, Serial No. 147,619

7 InGreat Britain 25, 1938 i 9 Claims. (Illa-27.5) I o This inventionrelates to cathode ray tubes emtion of the metal layer to the mosaicscreen as ploying photo-electric mosaic screens. referred to above.

Cathode ray tubes of this kind are employed in A further object of thepresent invention is to television systems, an image of the object forprovideanimproved methodofproducinga cath- '5 transmission beingprojected upon the mosaic ode ray tube employing a photo-sensitivemosaic screen which is scanned by a, cathode ray to proscreen'in whichthe amount of silver or other suitduce picture signals for transmission,able metal which is deposited on the screen for In the manufacture ofsuch tubes a support the purpose above-mentioned can be correctly suchas a plate of mica or other suitable material determined.

10 is mounted within the tube, such mica plate hav- According to onefeature of the invention, a 1 ing a layer of silver provided thereonwhich is cathode ray tube is provided having within the subsequentlyheated to uch a, tem erature that envelope one or more sources of silveror other the layer of silver aggregates into minute globules, suitablemetal such as tantalum, molybdenum, Associated with the mica sheet is aconductive iron, tung t n, Pl n k c p 8 1 signal plate which,'inconjunction with the silver is so disposed in relation to the mosaicscreen or 15 globules, forms a. multiplicity of small condensers. asupport on which said screen is formed and The aggregated silver layeris subsequently photoapab of being at 50 at t e Silver 0 ot ersensitised so that on the projection of an image metal can be evaporatedon to the screen or the on to the mosaic screen so formed, the minute aiS pport durin manufacture of the tube or condensers acquireelectrostatic charges accordsu eq e ly during e fe thereof. 20 ing tothe photo-electrons emitted in dependence According to n th r fe ur thei v n -1 H on the light and dark portions of the image, these comprisesa method of producing cathode ray minute condensers being restored to adatum potubes employing photo-electric mosaic screens in tential onscanning the screen with the cathode an evacuated envelope and in whichathin layer 5 ray. of silver or other suitable metalis adapted to be Thesilver surface which is applied to the mica deposited over substantiallythe whole of that suris usually formed thereon prior to assembling theface of the screen on which the elements are mica support in the tube,formed, comprising the step of determining, after In the specificationof British Patent No. evacuation and sealing of the envelope, the cor-458,586, it has been suggested to apply a thinrect amount of metal to bedeposited by project- 30 layer 01' metal over substantially the whole ofthe ing an image on to the screen, scanningthe screen surface of themosaic screen on which the phototo produce picture signals, reproducingpicture electric mosaic elements are formed. Such a signals and causingthe metal to be deposited on method serves to improve the insulationbetween to the screen during production of the picture 5 thephoto-electric elements of a mosaic screen signals, and'until thereproduced picture acquires 5 and additionally the photq-sensitivity ofthe mo-' the requireddegree of sharpness. After the corsaic screen isimproved without increasing the, rect amount of metal is deposited, thetube may amount of secondary emission obtained when the be subsequentlyheated at a temperature of the Y screen is bombarded with an electronbeam. order of 100 degs. to 200 degs. 0., and in cases 40 The quantityof silver or other suitable metal where silver is employed as the metal,satisfactory 40 which is deposited on the mosaic screen has to beresults are obtained at temperatures between 170 regulated verycarefully, since, if too little metal degs. and 180 degs. C. y isdeposited, no effect on the insulation is ob- The'present invention;therefore, provides a tained, while if too much silver is deposited, thecathode ray tube in which the initial deposit of insulation isdecreased, since the metal in such silver or other suitable metal can beapplied to the as circumstances provides a conductive path bemica orother support for the screen while the tween the elements. With a tubehaving an inlatter is mounted in position in the tube and also correctamount of deposited silver or other suitprovides a construction of tubein which a deable metal, pictures reproduced from signals obposit ofsilver or other metal can be applied to tained from such a tube exhibita marked lack of the photo-sensitised elements while the tube is in 50detail and sharpness. operation for the above mentioned purpose.

It is one of the objects of the present inven- In order that the saidinvention may be clearly tion to provide an improved construction ofcathunderstood and readily carried into efiect, the I ode ray tube witha view to facilitating manufacsame will now be more fully described withreferture of the mosaic screen or to facilitate applicaence to theaccompanying drawing in which: so

ray tube constructed in accordance with the invention and suitableforcarrying into eflect the method hereinbefore referred to, and

Fig. 2 is a front elevation of the support employed for the metalsources shown in Fig. 1.

As shownin Fig. 1, the reference numeral I indicates the envelope of thetube which is provided with a bulbous portion and a tubular portion inwhich a cathode ray gun of known form is provided. In Fig. 1 only thecathode 2 and the first and second anodes 3 and l of the cathode 'gunare shown. A support 5 of mica or other suitable material is mounted inthe tube and associated therewith is a conductive signal plate 6, a leadfrom which is brought to the exterior of the tube for connection to anamplifier whereby the picture signals obtained on scanning the mosaicscreen which is formed on the 'mica support 5 can be amplified prior totransmission. The surface of the mica support 5 opposite to the surfaceadjacent to the signal plate 6 is provided with a layer of metal,preferably silver.

In accordance with one feature of the invention, for the purpose ofapplying the initial deposit of silver or other metal to the micasupport 5, one or more sources of metal are provided inside the envelopeI. In order to enable a uni- 1 form deposit of metal over the whole.area of the screen more than one metal source is provided and inaccordance with the preferred form of the invention two metal sources ofsilver are provided in the tube, one of which isshown in Fig.

but maintain the'supports 8 substantially at right 1. These silversources-are each in the form of a helix 1 of tungsten wire mounted on asupport 8, the support being preferably made of mica and mountedsubstantially at right angles to the plane of the screen support 5. Asshown in Fig. 2 each support 8 carries an additional helix 9 the purposeof which will be hereinafter referred to. Each helix is provided with acoating of silver either by electro-depositing the silver thereon or byapplying the silver by other suitable processes, such as by cathodesputtering. The helices may be connected in. series and brought toexternal contacts whereby they can be connected to a suitable source ofheating current so that on'heating the helices the silver is vaporatedonto the surface of the support 5. The

support 8 may be shaped as shown in Fig. l in order substantiallytoprevent deposition of the silver on the parts where silver is notrequired, particularly onto that part of the tube through which theimage is projected. The two sources are mounted adiacent to the verticaledges of the support 5 and are arranged as shown in Fig. 2. This figureillustrates the construction of a supporting frame for the helices, theframe being arranged to be collapsibleso that it can be inserted througha narrow opening in the envelope I and erected in the form shown in Fig.2. As

stated above, the supports-8 are preferably made of mica and at theirupper edges they are provided with metal plates I0 riveted thereto, the

upper ends of the-supports 8 being maintained when in the erectedposition at the required distance apart by a strut II the ends of whichare provided with metal plates l2 riveted thereto and attached totheplates, II by flexible metal strips Illa. V

The strips |0a permitthe framework to be collapsed on moving thesupports 8 outwardly,

angles to the strut II when erected. The helices 1 are mounted on thesupports 8 through the order to aid in maintaining the framework in therequired position. It will be seen that metal sources are placed on theouter surfaces of the supports 8 so that on projection of the image fortransmission on to the screen 5, there islittle possibility of shadowsbeing formed on the screen due to the presence of the metal sources.

In practice, sufilcient silver will be applied to the helices 1 so thaton evaporating the whole of the silver deposited thereon, the requiredamount of silver will be applied to the support 5. By the arrangementdescribed, the elements can be mounted within the tube prior to thedeposition of silver on to thesupport 5, thus facilitating manufactureand avoiding possibility of damage compared with the known constructionon which the support is provided with its deposition of silver prior tomounting within the tube.

In another form of the invention, instead of employing a number of metalsources for providing uniformity in the deposited layer, an annulus orother suitably-shaped source may -be provided substantially surroundingthe said screen. Further, instead of plating or otherwise coating theaforesaid helices with silver, beads of silver or other suitable metalmay be provided within the convolutions of the helices. In

- seals will be required compared with a construction in which all thefilaments or meshes are. heated separately. The grids, instead of havingmetal mechanically attached thereto, may be electro-plated with therequired metal or may have the metal evaporated thereon. Alternative ly,metal plates, to which the required metal is attached or which areplated with the required adapted to be heated by eddy currents to evap-.

. orate the metal.

In the production of a tube after the silver from the sources I isdeposited on the support 5, the tube is heated atabout a temperature of650 degs. C. to cause aggregation of. the silver. Such globules aresubsequently oxidised in known manner and thereafter a photo-sensitivematerial, such as caesium, is introduced, preferably to a slight excess,so that the sensitivity of the mosaic screen so formed is-reducedslightly below the maximum sensitivity obtainable. The tube may then beheated for a short time at a temperature ofabout degs. C. after which itis sealed from the evacuating pump.

Where it is desired to apply a layer of sliver of other suitable metalover the surface of the metal may be provided within the envelope andmosaic screen in accordance with thespeciflcatubeisdesignedsothattheinltiallnerofmetaltoiormthemosaicscreenisappliedfl'omthe interior of the tube. it is thenpreferred topmvide the additional metal sourca I for electing theadditional coating of metal in accordance with the aforesaid Britishpatent. In Hg. 2 it willbeseenthateachsupportlcan'iestwo helices l and!both oi'whichareprovidedwitha' vaporisable metal, one of each pair ofhelices m employed for initially coating the support I while the otherhelix of'each pair is employed for provlding the additional metal layer.The helices I and 9 are so electrically connected that either set can beheated as desired. Alternatively, the sources of metal for theadditional coating may be constructed in accordance with themodification hereinbefore referred to.

As stated above, when applying the additional layer of metal, it isdiiilcult to r gulate the quantity depositedon the screen and inaccordance with a further feature of the invention the cathode ray tubedescribed, since metal sources are provided within the tube, is capableof being operated during deposition of the additional metal 2:! layer inorder accurately to deposite the additional metal layer. In carryingthis feature of the invention into eflect, the tube described isconnected in circuit for operation and an image of an object isprojected on to the screen 5 where- 30, by picture signals are generatedon scanning the screen. The picture signals after amplification are fedto a receiving or monitoring tube and the helices or other sources ofmetal are heated until the picture reproduced in the monitoring tubeacquires the required degree of sharpness. Heating of the helices isthen discontinued. after which the tube may again be heated at atemperature of the order of 100 degs. to 200 degs. C. and, in most caseswhere the additional layer is silver, satisfactory results will beobtained at temperatures between 170 dogs. and 180 degs. C.

It will be understood that should the sensitivity of the tube decreaseduring its life, additional metal can be deposited on the screen toimprove the sensitivity thereof without the necessity of breaking downthe tube, since the required source of metal is provided within thetube.

In cases where the tube with the metal sources is only employed for thedeposition of the initial metal layer, which is subsequently aggregated,it is preferred, as stated above, to apply to the helices or other metalsources only sufiicient silver or other metal to form the requiredthickness on the screen support. In some cases, however, more metal thanis required for this initial layer may be provided so that the sourcescan subsequently be employed for providing the additional coating ofmetal on to the mosaic screen after the screen is photo-sensitised.

It will be appreciated from the above that the tube constructed inaccordance with the invention enables silver or other suitable metalto-be applied to the support for the screen or to the mosaic screen whenformed during the manufacture of the tubes, or, subsequently, during thelife thereof, and, in addition, enables silver or other suitable metalto be deposited in accordance with the above described method.

Various modifications may be made in my invention without departing fromthe general features and embodiments thereof and I desire, therefore,that any and all of such modifications which fall fairly withinvthespirit and scope of the hereinafter appended claims may be utilized.

I claim as my invention:

a 3 1. a method or producing when, tubes employing photo-electric mosaicscreens in an' evacuated envelope and in which a thin layer of silver orother suitable metal is adapted to be deposited over substantially thewhole of that surface of the screen on which the individualphoto-electric elements of the mosaic are formed, comprising the step ofdetermining, after evacuation and sealing of the envelope, the amount ofmetal to be deposited upon the photo-electric mosaic to increase thesensitivity and definition thereof to a maximum by projecting an imageon to the screen, scanning the screen to produce picture signals,reproducing the 'picture signals and causing the metal to be depositedon to the screen during production of the picture signals, andcontinuing such deposition until the reproduced picture acquires therequired degree of sharpness.

2. The method of preparing a photosensitive mosaic surface upon anelectrode within a cathode ray tube wherein a cathode ray beam forscanning is developed which comprises the steps of depositing aninsulating layer upon said electrode, depositing a continuous film ofconductive material upon the insulating layer, thermally reducing thefilm to produce a mosaic surface comprising a plurality of electricallyisolated formed particles each of substantially microscopic size,oxidizing the formed particles, photoelectrically sensitizing the formedparticles, thermally removing the photoelectric deposit from areasintermediate the formed particles, tracing the developed cathode raybeam across the formed mosaic surface to produce signals representativeof the surface condition, depositing additional conducting material uponthe mosaic surface simultaneously with the scanning operation, limitingthe period of deposition of the second conducting material in accordancewith observations 'of the signals resulting from scanning, andsubsequently heating the formed mosaic over a temperature range of theorder of to 200 C.

3. The method of preparing a photosensitive mosaic surface upon aninsulating target electrode within a cathode ray tube wherein a cathoderay beam for scanning is developed which comprises the steps ofpositioning the target electrode within the tube envelope, depositing acontinuous film of conductive material upon the target electrode,thermally reducing the film to form a plurality of electrically isolatedparticles each of substantially microscopic size, oxidizing the formedparticles, photoelectrically sensitizing the formed photoelectric mosaicsurface, thermally removing the photoelectric deposit from areasintermediate the formed particles, tracing the developed cathode raybeam across the formed mosaic surface to produce signals representativeof the surface condition, depositing additional conducting material uponthe mosaic simultaneously with. the scanning operation, limiting theperiod of deposition of the second conducting material in accordancewith observations of the signals resulting from scanning, andsubsequently heating the formed mosaic over a temperature range of theorder of 100 to 200 C.

4. The method of preparing a photosensitive mosaic surface upon aninsulating target electrode within a cathode ray tube wherein a cathoderay beam for scanning is developed which comprises the steps ofdepositing a continuous film of conductive material upon the targetelectrode, thermally reducing the film to produce a mosaic surfacecomprising a plurality of elec- 5 trically isolated formed particleseach of substantially microscopic size, oxidizing the formed particles,photoelectrically sensitizing the formed photoelectric mosaic surface,removing the photoelectric deposit from areas intermediate the formedparticles, scanning the mosaic surface with the developed cathode raybeam, depositing additional conducting material upon the mosaic surfacesimultaneously with the scanning operation, limiting the period ofdeposition of the second conducting material in accordance withobservations of the signals resulting from scanning, and subsequentlyheating the formed mosaic.

5. The method of improving the sensitivity of mosaic'electrodestructures formed from photoelectrically sensitized isolated metallicparticles supported upon a dielectric support base within an electrontube which comprises the steps of depositing a metal coating overpredetermined portions of the activated mosaic surface, scan ning duringpe 'ods of metal deposition, limiting the period of deposition of themetal, coating in accordance with observations of the signals resultingfrom scanning and subsequently heating at a low temperature.

6. The method of improving the sensitivity of a mosaic electrodestructure formed from photoelectricaliy sensitized isolated electricallyconducing metallic particles supported upon a dielectric support base.within an electron tube wherein a cathode ray beam for scanning isdeveloped to form a mosaic surface which comprises the steps of tracingthe developed cathode ray beam across the formed mosaic surface,depositing additional conducting material upon the mosaic surfacesimultaneous with the scan-'- ning operation, limiting the period ofdeposition of the second conducting material in accordance withobservations of the signals resulting from scanning, and subsequentlyheating the base to a temperature within a temperature range of theorder of 100? to 200 C.

7. The process of forming a mosaic light sensitive surface onanon-conducting-base within a cathode ray tube wherein a cathode raybeam for scanning is developed which comprises applying to the base ametallic coating, thermally converting the coating into a plurality ofisolated metallic particles each microscopic in size to form a mosaicsurface, photosensitizlng the individual isolated metallic particles,tracing the developed cathode ray beam across the formed mosaic surface,depositing an additional metallic coating upon the mosaic surfacesimultaneously with the scanning operation, limiting the period ofdeposition of the second conducting material in accordance withobservations of the signals resulting from scanning, and subsequentlyheating the formed mosaic over a temperature range of the order of 100to 200 C.

8. The process of forming a mosaic light sensitive surface upon anon-conducting base within an electron tube which comprises applying ametal compound to the base, reducing the compound to form a mosaicsurface of isolated metallic particles microscopic in size by theapplication of heat, applying a layer of alkali metal upon the surfaceof the base, removing the alkali metal between the particles, depositingan additional metal compound coating over predetermined portions of theactivated mosaic surface, scanning during periods of metal deposition,limiting the period of deposition of the additional metal coating inaccordance with observations of the signals resulting from scanning andsubsequently heating at a low temperature.

9. The method according to claim 1, wherein after such an amount ofmetal has been deposited .as will ultimately produce maximum sensitivityand definition, the tube is heated to a temperature on the order of 100to 200 C.

LEONARD KLATzow.

